Ethylene polymerization using catalyst of controlled particle size

ABSTRACT

A process for producing particle-form olefin polymer in which the size of the silica-supported chromium oxide catalyst is selected to regulate the molecular weight distribution of the polymer.

ite States atet Donald R. Witt Bartlesville, Okla.

July 10, 1969 Nov. 30, 1971 Phillips Petroleum Company lnventor Appl. No. Filed Patented Assignee ETHYLENE POLYMERIZATION USlNG CATALYST 0F CONTROLLED PARTICLE SIZE 5 Claims, No Drawings [56] References Cited UNITED STATES PATENTS 3,225,023 12/1965 Hogan et al 260/949 3,288,767 I 1/1966 Hogan et al.... 260/882 Primary Examiner-Joseph L. Schofer Assistant Examiner--A. Holler AttorneyYoung and Quigg ABSTRACT: A process for producing particle-form olefin polymer in which the size of the silica-supported chromium oxide catalyst is selected to regulate the molecular weight distribution of the polymer.

ETHYLENE POLYMERIZATION USING CATALYST F CONTROLLED PARTICLE SIZE This invention pertains to olefin polymerization. In one of its more specific aspects, this invention pertains to molecular weight distribution, the narrower the distribution, the smaller the change in shear rate with change in applied shear stress. Conversely, the wider the molecular weight distribution, the greater the change in shear rate with change in olefin polymers produced by catalytic polymerization of a lapplied shear stress. olefin over a supported catalyst. .The molecular weight distribution of a polymer is generally Use of supported catalysts for the polymerization of olefins, expressed as the ratio of its weight average molecular weight, particularly l-olefins, and particularly ethylene, is well- M,,, to the number average molecular weight, M However, known. The polymer can be produced in the form of a solution this ratio, M /M, is also proportional to the ratio of its highor in the form of a solid existing asaslurry in aliquid medium. load melt index, HLMI, to its regular melt index, Ml. Acln one method, a chromium oxide-containing catalyst is emcordingly, then, the shear response and molecular weight disployed. Depending upon the reaction conditions employed, tribution of a polymer is reflected in the ratio between its highcertain properties of the polymer, such as melt index can be load melt index and its regular melt index. vflfled- It has now been ascertained that certain of the shear proper- It has now been discovered that polymer of selected prop rties of a polymer are related to the particle size or related proties can be produced by controlling the particle size of the perties of the catalyst used in the production of the catalyst. catalyt P y B to the method of lhl5 io This is indicated by the fact thal under the conditions of comthe is pr id in he pr ces f r the ca lytic polymenzaparatively constant melt index, the high-load melt index varies of olefill to Produce a P y e p t e Said with the catalyst particle size and properties related thereto. P pl y Preferably p l' 'f pp Specifically, it has been found that molecular weight distribu- 2: 3:22:rz gsszflsz ifg zzi oggamc dllluem at 3 tion of the composite polymer produced in the polymerizaltion 0 e a P lc P y a5 a recess broadens, as indicated by the ratio of the highoad y. the improvement comprising selecting the Particle Size :ielt index (HLMl-ASTM D 1,238-571, Condition F) to melt of the catalyst employed to control the rheological properties index (MLASTM D 13 471" Condition E), as the panide of lthetplolymertprodutcet h I I size of the catalyst increases. While it is known that catalyst ht Z, :2? o f I; t S t F mo if particle size afi'ects reaction rates and that certain particle size welg n u on o e Po ymer pro measure an catal sts are referentiall em lo ed for other reasons the average particle size of the catalyst is increased if the heretifore it g not been s f the molecular weigh; average molecular weight distribution decreases and: converdistribution of the Polymer would be afiecte sely, decreased if the average molecular weight distribution in- It has been found, for example that a polymer of relafivdy i gf s fissg a polymer havmg a regulated molecular narrow molecular weight distribution is obtained when using catal st articles of 325 mesh or finer. Under the same condi- Accordingly, it is an ObjCCl of this invention to provide a tionsya zatalyst having a particle Size of about 140 mesh or ws a glggfig polymers having controllable molecular coarser produces a polymer of much broader molecular lt is another object of this invention to minimize Polymer Pleight distribution g gg g i an g slze' or example, a out 2 0 mes size, pro uce a po ymer gzw sgf g gfr m that product produced from a Smgle with an intermediate molecular weight distribution. ()rdinarily These and ('nher objects of this invention will become catalyst particles coarser than about 20 mesh are not used. evident from the following discussion 40 However, catalysts of any particle size, even smaller than 325 i mesh can be used.

The process to which the present invention is particularly applicable is that generally described in British Pat. No. In F i the molecular wedght dlsmbuuon i the 853 4l4 and is generally known as particle-form polymerizapolymerizanon product can be comlimoufly measured In any tion process. In that process, at least one olefin is polymerized @nvemlonal "T and an appropnate lgnal can be reiayed at a temperature in the range of about 150 F. to about 230 F. wlth a conventional controller to zippropmiie valves on p of by the catalyst consisting essentially of chromium oxide on catalyst hfwmgfelauvely smanflmtrmedlmeiand relatively supports such as silica silica-alumina alumina zirconia large f i size Thus to malmam deslred. moiecular thoria at least a portion of the chmmium being the weight distribution level. catalysts of specific particle size, or avalent state at the initial contact between the olefin and 0 t g can be Introduced mm the reacnon zone m a catalyst. The catalyst is maintained in suspension and is con- 2: g t h l t f t I t tacted with the olefin in an organic medium at pressures suffi- 0 gfmera e ee 0 ca 3 l cient to maintain the medium in the liquid phase. The medium pamlc e slze e o i a g and temperature are such that the polymer produced is insoluf g a g if s 9 f; e f:- ble in the medium and is recovered in the form of solid partime as e meta 9 avlson a e from Davison Chemical Division, W. R. Grace and Company, cles.

The product produced by the polymerization consists of a lndustnal Chemicals Dept, Balt1more, Md., was screened to mixture of polymers which mixture exhibits properties obtain the catalyst sizes shown. In each instance, ethylene was proximating an average of those properties possessed by the Polymenzed m Isobutane 'i and j individual polymers of the mixture. In other words, the total the i f having been emlvated pi to polymerization at product polymer produced from any Po'Ymerization is one in 1,600 F. in the conventional manner. Essentially identical which there are various percentages of the various component were three ranges 9 catalyst mesh In the polymers on the basis of which the total polymer exhibits runs tabulated in table I, the melt index values have been obpenies which represent the average propel-ties f the polymers tained at substantially the same polymer production rates in contained h i 5 terms of pounds of polymer per pound of catalyst. Results The shear response of a polymer is largely a function of its were asfonowsi TABLE I Catalyst properties Polymer properties Hexavalont High load Surlace Pore Pore chromium Regular A melt Run Mesh size, U.S. area, volume, diameter, content, melt index, IILMI/ No. Standard Series mfi/g. ceJg. A percent index, MI HLMI MI Finer than 325- 267 1.51 226 0.75 1.02 60 8 59.6 200 to 300- These data indicate the operability of the method of the present invention in controlling molecular weight distribution of the polymer by selecting the size of the catalyst particles employed in the reaction. These data further illustrate that as the particle size of the catalyst is increased, the ratio of highload to regular melt index is increased showing that the molecular weight distribution of the polymer produced is broadened.

The method of this invention has wide applicability in commercial production and can be employed over any selected range of melt indices. lt permits establishing a reaction zone into which olefin is continuously introduced and polymer continuously withdrawn, the molecular weight distribution of the polymer product being controlled by varying the particle size of the catalyst introduced into the reactor, wither periodically or continuously with the olefin feed. lnasmuch as the molecular weight distribution of polymer evidences itself in specifically determinable properties such as shear response, the method of this invention provides a means of producing in a single continuous operation or in a series of batch operations, a blend of polymers of individual properties which impart to the total polymer properties not otherwise obtainable.

It will be evident from the above discussion that certain modifications can be made to this invention. However such are considered to be within the scope of the invention.

What is claimed is:

l. A process for producing a particle-form polymer of regulated molecular weight distribution obtained by polymerizing a l-olefin in a reaction zone in the presence of a supported polymerization catalyst comprising an oxide of chromium and a support of at least one oxide selected from the group consisting of silica, alumina, zirconia and thoria. which comprises determining the average molecular weight distribution of the polymer produced and increasing the average particle size of the catalyst if the molecular weight distribution decreases and decreasing the average particle size of the catalyst if the average molecular weight distribution increases and thereby obtaining a polymer of said l-olefin having a regulated molecular weight distribution.

2. The process as defined in claim 1 in which the catalyst mesh size is from about 20 to about 500 mesh. U.S. Standard Sieve Series.

3. The process as defined in claim 1 in which the catalyst comprises chromium oxide supported on a silica base.

4. The process as defined in claim 1 in which the catalyst mesh size is from about I00 to about 325 mesh, U.S. Standard Sieve Series.

5. The process as defined in claim 1 in which the polymer has an HLMl/Ml ratio within the range of from about 60 to about and a melt index within the range of from about 1.00 to about 1.10. 

2. The process as defined in claim 1 in which the catalyst mesh size is from about 20 to about 500 mesh, U.S. Standard Sieve Series.
 3. The process as defined in claim 1 in which the catalyst comprises chromium oxide supported on a silica base.
 4. The process as defined in claim 1 in which the catalyst mesh size is from about 100 to about 325 mesh, U.S. Standard Sieve Series.
 5. The process as defined in claim 1 in which the polymer has an HLMI/MI ratio within the range of from about 60 to about 80 and a melt index within the range of from about 1.00 to about 1.10. 